Refrigerator

ABSTRACT

The purpose of the present invention is to provide a refrigerator in which the capacity of an oil tank can be made smaller than in the prior art while a foaming phenomenon is addressed. The refrigerator is provided with: a refrigeration cycle which includes a condenser, an evaporator, and an electric compressor having a compression mechanism to be driven by a motor and in which a refrigerant circulates; an oil tank in which a lubricating oil is stored; a heater which is set in the oil tank and which heats the lubricating oil; a lubricating oil supply line which is connected to the oil tank and which supplies the lubricating oil from the oil tank into a housing having the motor housed therein; a lubricating oil discharge line which returns the lubricating oil from the housing back to the oil tank; a pressure equalizing pipe which has one end connected to the oil tank and the other end connected to the refrigeration cycle; and a buffer tank which is set to the pressure equalizing pipe, which receives the refrigerant and the lubricating oil flowing out from the oil tank, and in which the lubricating oil is stored.

TECHNICAL FIELD

The present invention relates to a chiller.

BACKGROUND ART

A turbo compressor installed in a centrifugal chiller is configured toinclude a compression mechanism and an acceleration mechanism. In orderto stably operate the turbo compressor, it is necessary to properly andcontinuously supply a lubricant to a bearing for supporting an impellerof the compression mechanism or a gear of the acceleration mechanism. Alubricant system includes an oil tank and an oil pump. The lubricantstored in the oil tank is supplied to the bearing or the gear of theturbo compressor by the oil pump. The lubricant supplied to the bearingor the gear is returned to the oil tank so as to be repeatedlycirculated in the lubricant system.

In the compression mechanism, the refrigerant system and the lubricantsystem are not completely independent of each other. Accordingly, therefrigerant dissolves in the lubricant. If the refrigerant dissolves inthe lubricant, viscosity decreases. Thus, in order to reduce thedissolving amount of the refrigerant in the oil tank, the oil tank isinternally maintained at low pressure. Therefore, for example, apressure equalizing pipe communicating with a low pressure portion (forexample, an evaporator or a compressor suction port) of the refrigerantsystem is connected to the oil tank.

PTL 1 below discloses a technique as follows. When the centrifugalchiller is started, the pressure inside the oil tank is lowered, and therefrigerant dissolving in the lubricant is gasified to cause foaming.Accordingly, a target opening degree is provided for a suction capacitycontrol unit for controlling capacity of the refrigerant passing throughthat the turbo compressor when the centrifugal chiller is started. Inaddition, PTL 2 below discloses a technique as follows. The other end ofthe pressure equalizing pipe whose one end is connected to the oil tankis connected to an economizer instead of the evaporator so that theinternal pressure of the oil tank and the internal pressure of theeconomizer are equalized.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No.2009-186030

[PTL 2] Japanese Unexamined Patent Application Publication No.2009-293901

SUMMARY OF INVENTION Technical Problem

The internal pressure is lowered in the oil tank communicating with therefrigerant system, when the centrifugal chiller in which the pressureof the refrigerant system is lowered starts to be operated or is in atransition stage. Here, the transition stage means a time at which anoperation state is changed, for example, such as a case of lowering anoutput of the centrifugal chiller. If the internal pressure of thelubricant system is lowered, such as in a case where the internalpressure of the oil tank is lowered, the refrigerant dissolving in thelubricant no longer dissolves beyond a saturated state, and refrigerantgas is generated, thereby causing a foaming phenomenon in which thelubricant forms bubbles.

Inside the oil tank where the foaming phenomenon occurs, the oil levelrises, compared to a normal time during which the foaming phenomenondoes not occur. In addition, if the foaming phenomenon occurs, thesupply amount of the lubricant which can be supplied to a bearing or agear is reduced in the lubricant system. In a case of a low pressurerefrigerant (for example, R1233zd), a refrigerant gas specific volume islarger than that of a high pressure refrigerant (for example, R134a).Accordingly, a large volume of the gas is generated during the foamingphenomenon. Therefore, in a case of the low pressure refrigerant, whenthe oil level rises or the supply amount of the lubricant is reduced,there is a greater difference, compared to the normal time.

The pressure equalizing pipe connected to the oil tank is connected toan upper portion of the oil tank. However, the lubricant having thefoaming is caused to flow into the pressure equalizing pipe due to theoil level rising during the foaming, thereby causing a possibility thatthe lubricant may flow to the evaporator which is a connectingdestination of the pressure equalizing pipe. Therefore, in the relatedart, in order to cope with the oil level rising during the foaming, aheight of the oil tank is increased.

In addition, while a depth of the oil tank is increased, and the oilpump is located on a bottom surface of the oil tank so that the oil pumpdoes not suction the refrigerant gas during the foaming. In this manner,the oil level when the foaming occurs and a position of the oil pump areseparated from each other.

In any case, it is necessary to increase a size of the oil tank in aheight direction, and the large capacity of the oil tank has to be setin order to cope with the foaming phenomenon.

The present invention is made in view of the above-describedcircumstances, and an object thereof is to provide a chiller which cancope with a foaming phenomenon and can decrease capacity of an oil tank,compared to that in the related art.

Solution to Problem

In order to solve the above-described problems, a chiller according tothe present invention adopts the following means.

That is, according to the present invention, there is provided a chillerincluding a refrigerating cycle that includes an electric compressorhaving a compression mechanism driven by a motor, a condenser, and anevaporator, and in which a refrigerant is circulated, an oil tank thatstores a lubricant, a heater that is installed inside the oil tank so asto heat the lubricant, an oil circulation pipe that is connected to theoil tank so as to supply the lubricant from the oil tank into a housingfor accommodating the motor and to return the lubricant from the housingto the oil tank, a pressure equalizing pipe, one end of which isconnected to the oil tank, separately from the oil circulation pipe, andthe other end of which is connected to the refrigerating cycle, and abuffer tank that is installed in the pressure equalizing pipe, and thatreceives the refrigerant and the lubricant which flow out of the oiltank so as to store the lubricant.

According to this configuration, the motor for driving the compressionmechanism is accommodated in the housing, and the lubricant is suppliedfrom the oil tank to the housing. Accordingly, a bearing for supportinga rotary shaft of the motor can be lubricated with the lubricant. Inaddition, one end of the pressure equalizing pipe is connected to theoil tank, and the other end of the pressure equalizing pipe is connectedto the refrigerating cycle. Therefore, pressure of a portion connectedto the refrigerating cycle and internal pressure of the oil tank aresubstantially equalized. A portion to which the pressure equalizing pipeis connected in the refrigerating cycle is a portion where the pressureis low in the refrigerating cycle, for example, such as an evaporatorand a compressor suction port.

Furthermore, the refrigerant and the lubricant which flow out of the oiltank are supplied to the buffer tank via the pressure equalizing pipe,and are temporarily stored in the buffer tank. In this manner, even iffoaming occurs inside the oil tank and the refrigerant and the lubricantflow out of the oil tank, the lubricant is stored in the buffer tank,and does not flow to the refrigerating cycle. Accordingly, only therefrigerant is guided toward the refrigerating cycle.

In the above-described invention, the chiller may further include areturn pipe, one end of which is connected to the buffer tank, and theother end of which is connected to the oil tank, separately from thepressure equalizing pipe, and that returns the lubricant stored in thebuffer tank to the oil tank.

According to this configuration, one end of the return pipe is connectedto the buffer tank, and the other end of the return pipe is connected tothe oil tank so that the lubricant stored in the buffer tank is returnedto the oil tank. In this manner, the lubricant flowing out of the oiltank and accumulated in the buffer tank is returned to the oil tankwithout flowing into the refrigerant cycle.

In the above-described invention, a position where the return pipe isconnected to the oil tank may be located on a side close to a positionwhere the oil circulation pipe is connected to the oil tank.

According to this configuration, the lubricant returned from the buffertank is returned to the vicinity of the position where the oilcirculation pipe is connected to the oil tank. Accordingly, even in acase where the foaming occurs inside the oil inside the oil tank 23, thelubricant returned from the buffer tank is mixed with the lubricantwhich is not affected by the foaming.

In the above-described invention, the oil tank may be partitioned by apartition plate, and may be divided into a separation region into whichthe lubricant returned from the housing flows, and a discharge regionthrough which the lubricant is supplied to the housing.

According to this configuration, the lubricant having the dissolvedrefrigerant is supplied to the separation region, and the lubricanthaving the dissolved refrigerant is separated into the lubricant and therefrigerant in the separation region. Then, the separated lubricant issupplied from the separation region to the discharge region, and issupplied into the housing. The separation region and the dischargeregion are partitioned by the partition plate. Accordingly, in theseparation region, the lubricant flowing into the oil tank isefficiently separated using a difference between the lubricant and therefrigerant or an enclosed space. In addition, even if the foamingphenomenon occurs in the separation region, it is possible to preventthe lubricant having the bubbles formed therein from flowing into thedischarge region.

In the above-described invention, a flow forming plate for guiding aflow of the lubricant stored in the oil tank from an upper portiontoward a lower portion or from the lower portion toward the upperportion may be installed in the separation region.

According to this configuration, it is possible to form a flow guidedfrom the upper portion toward the lower portion inside the storedlubricant, or conversely to form a flow guided from the lower portiontoward the upper portion.

In the above-described invention, the partition plate may be installedaway from a bottom surface of the oil tank.

According to this configuration, the lubricant having the dissolvedrefrigerant flows to a downstream side without staying in a bottomportion inside the separation region.

Advantageous Effects of Invention

According to the present invention, it is possible to cope with afoaming phenomenon and to decrease capacity of an oil tank, compared tothat in the related art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating a centrifugal chilleraccording to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view illustrating a turbo compressorof the centrifugal chiller according to the embodiment of the presentinvention.

FIG. 3 is a perspective view illustrating an oil tank of the centrifugalchiller according to the embodiment of the present invention.

FIG. 4 is a perspective view illustrating a modification example of theoil tank of the centrifugal chiller according to the embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a centrifugal chiller 1 according to an embodiment of thepresent invention will be described with reference to the drawings.

As illustrated in FIG. 1, the centrifugal chiller 1 includes a turbocompressor 2 which compresses a refrigerant, a condenser 3 which coolsand condenses the refrigerant, a sub-cooler 4 which re-cools and appliessuper-cooling to the refrigerant condensed in the condenser 3, a firstpressure-reducing valve 5 which reduces pressure of a high pressurerefrigerant to be intermediate pressure, an economizer 6 which appliesthe super-cooling to the refrigerant, a second pressure-reducing valve 7which reduces the pressure of the refrigerant to be low pressure, and anevaporator 8 which evaporates a low pressure refrigerant.

The turbo compressor 2, the condenser 3, the sub-cooler 4, the firstpressure-reducing valve 5, the economizer 6, the secondpressure-reducing valve 7, and the evaporator 8 configure arefrigerating cycle. The refrigerant is circulated in order of the turbocompressor 2, the condenser 3, the sub-cooler 4, the firstpressure-reducing valve 5, the economizer 6, the secondpressure-reducing valve 7, and the evaporator 8. The refrigerant issupplied from the economizer 6 to the turbo compressor 2 using a bypasswithout passing through the evaporator 8.

The turbo compressor 2 includes a housing 30 configured so that a motorhousing 31, an accelerator housing 32, and a compressor housing 33 arecombined integrally with each other.

As illustrated in FIG. 2, a motor 9 driven so that variable speed isallowed by an inverter device is incorporated in the motor housing 31.One end 10 a of the motor shaft 10 of the motor 9 protrudes from themotor housing 31 to the accelerator housing 32. The motor 9 includes astator 20 and a rotor 21. The rotor 21 is fixed to the motor shaft 10,and the rotor 21 is rotated inside the stator 20. The motor shaft 10 issupported by the rolling bearing 14 on the side of the acceleratorhousing 32. The rolling bearing 14 has a plurality of angular ballbearings, for example. The rolling bearing 14 is installed in the motorhousing 31 via a bearing box (not illustrated).

The compressor housing 33 internally accommodates a compressionmechanism 15 having a first stage compression stage and a second stagecompression stage. The refrigerant suctioned into the first stagecompression stage from the outside and compressed by the first stagecompression stage is supplied to the second stage compression stage.Then, the refrigerant, suctioned into the second stage compression stageand compressed by the second stage compression stage is dischargedoutward.

A rotary shaft 11 is rotatably installed inside the compressor housing33. One end 11 a side of the rotary shaft 11 has a first stage impeller12 for the first stage compression stage and a second stage impeller 13for the second stage compression stage. The rotary shaft 11 is supportedby a rolling bearing 14 on a side of the accelerator housing 32. Forexample, the rolling bearing 14 includes a plurality of angular ballbearings. The rolling bearing 14 is installed in the compressor housing33 via a bearing box (not illustrated).

The other end 11 b side of the rotary shaft 11 supported by the rollingbearing 14 has a small diameter gear 17. The gear 17 meshes with a largediameter gear 18 disposed in one end 10 a of the motor shaft 10. Thesegears 17 and 18 configure an acceleration mechanism 19. The accelerationmechanism 19 is accommodated in the accelerator housing 32.

In the rolling bearing 14 and the gears 17 and 18, a lubricant issupplied to each component.

A lubricant system is configured to include a lubricant supply line 22and a lubricant discharge line 25.

The lubricant supply line 22 is a pipe for connecting the oil tank 23and the turbo compressor 2 to each other. The lubricant is supplied fromthe oil tank 23 to the motor housing 31 of the turbo compressor 2 andthe accelerator housing 32 by an oil pump 36 disposed in the lubricantsupply line 22. The lubricant passing through the motor 9 and theacceleration mechanism 19 is returned to the oil tank 23 via thelubricant discharge line 25. An oil cooler 24 is installed in thelubricant supply line 22 and the lubricant discharge line 25 accordingto the present embodiment.

The motor housing 31 and the accelerator housing 32 have each lubricantinlet connected to the lubricant supply line 22, and the lubricant issupplied from the lubricant supply line 22 to the turbo compressor 2.The refrigerant extracted from the condenser 3 which configures therefrigerating cycle is supplied to the turbo compressor 2. The motorhousing 31 and the accelerator housing 32 have each liquid refrigerantinlet connected to a refrigerant supply line 34, and a liquidrefrigerant is supplied from the refrigerant supply line 34.

The lubricant passing through the inside of the motor housing 31 and theinside of the accelerator housing 32 of the turbo compressor 2 isdischarged to the oil tank 23. The motor housing 31 and the acceleratorhousing 32 have each lubricant outlet connected to the lubricantdischarge line 25. The refrigerant and the lubricant are discharged fromthe motor housing 31 and the accelerator housing 32 to the oil tank 23via the lubricant discharge line 25.

In the lubricant discharged to the oil tank 23, the refrigerantdissolves, and the lubricant is diluted by the refrigerant. A heater 27(refer to FIG. 3) for evaporating the refrigerant in order to increaseconcentration of the diluted lubricant is installed in the oil tank 23.Since the refrigerant is evaporated, kinematic viscosity of thelubricant returns to a state before the lubricant is diluted. Thus, thelubricant can be repeatedly used as the lubricant for lubricating thegears 17 and 18 and the rolling bearing 14.

As illustrated in FIG. 3, the oil tank 23 is a container capable ofaccommodating the lubricant, and the lubricant is stored in a lowerportion inside the oil tank 23.

The oil tank 23 can be roughly divided into a separation region 41 and adischarge region 42.

The oil tank 23 has a lubricant and refrigerant inlet connected to thelubricant discharge line 25. For example, the heater 27 is installed ina lower portion of the separation region 41 of the oil tank 23. Therefrigerant and the lubricant inside the oil tank 23 are heated so as toevaporate the refrigerant. In this manner, refrigerant gas generated byevaporation is guided upward of the oil tank 23, and the lubricanthaving reduced content of the refrigerant after the refrigerantevaporates flows to a downstream side of the oil tank 23.

A lubricant outlet connected to the lubricant supply line 22 is formedbelow the oil tank 23. According to the present embodiment, the oil pump36 is installed in the lubricant outlet. The lubricant is supplied fromthe oil tank 23 to the turbo compressor 2 via the lubricant supply line22.

In addition, a refrigerant gas outlet connected to the pressureequalizing pipe 29 is formed above the oil tank 23, and the refrigerantgas is supplied from the oil tank 23 to the evaporator 8 via thepressure equalizing pipe 29. In this manner, the refrigerant supplied tothe turbo compressor 2 from the condenser 3 and the sub-cooler 4 isreturned to the refrigerating cycle.

In addition, one end of the pressure equalizing pipe 29 is connected tothe oil tank 23, and the other end of the pressure equalizing pipe 29 isconnected to the evaporator 8 of the refrigerating cycle. Accordingly,pressure of the evaporator 8 in a portion connected to the refrigeratingcycle and internal pressure of the oil tank 23 are substantiallyequalized. A connecting destination of the pressure equalizing pipe 29is not limited to the evaporator 8, and may be a suction port of theturbo compressor 2, for example.

It is preferable to adjust the lubricant stored inside the oil tank 23so as to maintain a predetermined temperature range. For example, thetemperature of the lubricant is determined, based on the temperature atwhich adequate lubrication can be achieved in the gears 17 and 18 andthe rolling bearing 14 in the turbo compressor 2 lubricated with thelubricant.

The temperature of the lubricant stored inside the oil tank 23 isadjusted, for example, by means of heating using the heater 27. Theheating using the heater 27 is controlled by the temperature measured bya temperature measuring unit 35 installed in a lower portion of the oiltank 23. Based on the measured temperature, turning on and off of theheater 27 may be controlled so as to adjust the heating of therefrigerant or the lubricant. Alternatively, based on the measuredtemperature, the setting temperature of the heater 27 may be adjusted.

The oil tank 23 is partitioned by a partition plate 43, and is dividedinto the separation region 41 and the discharge region 42. The partitionplate 43 is a plate-shaped member, and a side end portion is in contactwith an inner surface of the oil tank 23. In this manner, the oil tank23 is divided into two regions by the partition plate 43 serving as aboundary. The lubricant discharge line 25 side from the partition plate43 is the separation region 41 into which the lubricant returned fromthe housing 30 flows. In addition, the lubricant supply line 22 sidefrom the partition plate 43 is the discharge region 42 through which thelubricant is supplied to the housing 30.

The lubricant having the dissolved refrigerant is supplied from thelubricant discharge line 25 to the separation region 41. The lubricanthaving the dissolved refrigerant has higher specific gravity than thatof the refrigerant alone and the lubricant alone. The concentration ishigh on a bottom surface of the separation region 41. The refrigerant isheated and gasified by the heater 27 located close to the bottom surfaceof the separation region 41 having the high concentration of therefrigerant, and the lubricant having the dissolved refrigerant isseparated into the lubricant and the refrigerant. Inside the oil tank23, a space for storing the lubricant is limited by the partition plate43. Accordingly, the lubricant can be efficiently heated by the heater27.

The separation region 41 may have a plurality of flow forming plates 44other than the above-described partition plate 43. The flow formingplates 44 are installed in the separation region 41. In this way, insidethe stored lubricant, it is possible to form a flow in which thelubricant is guided from an upper portion to a lower portion, orconversely to form a flow in which the lubricant is guided from thelower portion to the upper portion. In this manner, the lubricant can beefficiently brought into contact with the heater 27, or the separatedand gasified refrigerant can be raised upward.

The heated and gasified refrigerant rises upward of the lubricant storedin the oil tank 23. Even in a case where a foaming phenomenon occurs,the lubricant having bubbles formed therein rises along the partitionplate 43 or the flow forming plate 44. Thereafter, the bubbles are in astate of floating on the liquid lubricant. Therefore, according to thepresent embodiment, unlike a case where the partition plate 43 and theflow forming plate 44 are not provided, the bubbles formed by therefrigerant gas are less likely to flow to the downstream side insidethe liquid lubricant. As a result, the bubbles can be prevented frombeing suctioned into the oil tank 23.

The lubricant stored inside the oil tank 23 is caused to flow in onedirection by the oil pump 36, that is, to flow from the lubricant andrefrigerant inlet side to the lubricant outlet side. In this manner, thelubricant whose refrigerant concentration is lowered by separating therefrigerant flows toward the lubricant outlet side. In addition, in acase where the foaming phenomenon occurs, the bubbles floating on thelubricant also flows toward the downstream side along the flow of thelubricant.

If the oil level is raised by the bubbles due to the foaming phenomenon,the bubbles pass through the inside of the pressure equalizing pipe 29,and the foamy lubricant falls into the buffer tank 28.

A lower end portion of the partition plate 43 or the flow forming plate44 may be in contact with the bottom surface of the oil tank 23, or maybe located away from the bottom surface. In a case where the lower endportion is in contact with the bottom surface, a flow from the lowerportion to the upper portion is formed in the lubricant. In a case wherethe lower end portion is located away from the bottom surface, thelubricant having the dissolved refrigerant flows to the downstream sidewithout staying in the bottom portion inside the separation region 41.In this case, the lubricant having the dissolved refrigerant flows alongthe heater 27. Accordingly, the refrigerant can be efficiently gasified.

In addition, in the example illustrated in FIG. 3, a case of installingone partition plate 43 and two flow forming plates 44 is illustrated.However, the present invention is not limited to this example. Forexample, as illustrated in FIG. 4, one partition plate 43 and one flowforming plate 44 may be installed.

The oil pump 36 is installed in the discharge region 42. For example,the oil pump 36 is an immersion pump, and is installed on the bottomsurface of the oil tank 23. The oil pump 36 suctions the lubricant inthe bottom portion of the oil tank 23, and supplies the lubricant to theoutside, that is, to the housing 30. According to the presentembodiment, in a case where the foaming phenomenon occurs, the bubblerises in the separation region 41. Therefore, the oil pump 36 installedin the discharge region 42 is less likely to suction the refrigerantgas.

The heater 27 may be installed in only the separation region 41 on theupstream side, or may also be installed in the discharge region 42 onthe downstream side as illustrated in FIG. 3. Since the heater 27 isinstalled in the discharge region 42, it is possible to increase theamount of the refrigerant separated from the lubricant. However, in acase where the foaming phenomenon may possibly occur due to the heatingusing the heater 27 in the discharge region 42, it is preferable not toinstall the heater 27 in the discharge region 42.

The buffer tank 28 is installed in the pressure equalizing pipe 29. Thebuffer tank 28 can store the foamy lubricant flowing out of the oil tank23, and has capacity not to allow the lubricant to flow out to thepressure equalizing pipe 29 on the downstream side. An upper portion ofthe buffer tank 28 has an inlet portion connected to the pressureequalizing pipe 29 connected with the oil tank 23. In addition, theupper portion of the buffer tank 28 has an outlet portion formed at aportion separate from the inlet portion. The outlet portion is connectedto the pressure equalizing pipe 29 connected to the evaporator 8.

The refrigerant and the lubricant which flow out of the oil tank 23 aresupplied to the buffer tank 28 via the pressure equalizing pipe 29.Then, the lubricant flowing out of the oil tank 23 is temporarily storedin the buffer tank 28. In addition, the gasified refrigerant dissolvingin the lubricant flows from the buffer tank 28 to the evaporator 8.

In this manner, even if the foaming occurs inside the oil tank 23 andthe foamy refrigerant and lubricant flow out of the oil tank 23, thelubricant is stored in the buffer tank 28, and does not flow to therefrigerating cycle. Only the refrigerant is guided to the refrigeratingcycle.

The return pipe 26 is connected to below the oil tank 23. In the returnpipe 26, for example, one end is connected to the bottom surface of thebuffer tank 28, and the other end is connected to the oil tank 23. Thereturn pipe 26 is disposed separately from the pressure equalizing pipe29, and returns the lubricant stored in the buffer tank 28 to the oiltank 23. In this manner, the lubricant flowing out of the oil tank 23and accumulated in the buffer tank 28 is returned to the oil tank 23without flowing to the refrigerant cycle.

A position where the return pipe 26 is connected to the oil tank 23 islocated on a side close to a position where the lubricant supply line 22is connected to the oil tank 23. In this manner, the lubricant returnedfrom the buffer tank 28 is returned to the vicinity of the positionwhere the lubricant supply line 22 is connected to the oil tank 23, forexample, to the discharge region 42. Accordingly, the lubricant returnedfrom the buffer tank 28 is mixed with the lubricant which is notaffected by the foaming, even in a case where the foaming occurs insidethe oil tank 23.

Next, a supply method and a cooling method of the lubricant in thecentrifugal chiller 1 according to the present embodiment will bedescribed.

The lubricant is stored in the oil tank 23, and is supplied from the oiltank 23 to the turbo compressor 2 by the oil pump 36. The lubricantsupplied to the turbo compressor 2 is supplied to the gears 17 and 18and the rolling bearing 14 inside the motor housing 31 of the turbocompressor 2 and inside the accelerator housing 32.

While the lubricant supplied to the gears 17 and 18 and the rollingbearing 14 is used in lubricating the gears 17 and 18 and the rollingbearing 14, the temperature of the lubricant rises due to a frictionloss.

The lubricant passing through the motor housing 31 and the acceleratorhousing 32 of the turbo compressor 2 is cooled after passing through theoil cooler 24. In this manner, the lubricant passing through the gears17 and 18 and the rolling bearing 14 inside the motor housing 31 and theaccelerator housing 32 of the turbo compressor 2 is cooled by the oilcooler 24.

Thereafter, the lubricant cooled by the oil cooler 24 and therefrigerant dissolving in the lubricant are discharged to the oil tank23.

The lubricant and the refrigerant which are discharged to the oil tank23 flows to the lower portion in the separation region 41, and is heatedby the heater 27 installed in the lower portion inside the oil tank 23so that the refrigerant evaporates. As a result, the kinematic viscosityof the lubricant diluted by the refrigerant is recovered.

The lubricant having reduced content of the refrigerant after therefrigerant evaporates flows to the downstream side of the oil tank 23.In addition, the refrigerant gas evaporated by the heater 27 is guidedupward of the oil tank 23. The refrigerant gas is supplied from the oiltank 23 to the evaporator 8 through the pressure equalizing pipe 29 andthe buffer tank 28.

In a case of the foaming phenomenon where the pressure inside the oiltank 23 is lowered due to the lowered pressure in the refrigeratingcycle and the refrigerant forms the bubbles due to the gasifiedlubricant, the bubbles formed by the refrigerant and the lubricant risealong the partition plate 43 or the flow forming plate 44. Furthermore,the bubbles floating on the liquid lubricant flow toward the downstreamside along the flow of the lubricant.

If the oil level is raised by the bubbles due to the foaming phenomenon,the bubbles pass through the inside of the pressure equalizing pipe 29,and the bubbles formed by the refrigerant and the lubricant fall intothe buffer tank 28. As a result, the lubricant is stored in the lowerportion inside the buffer tank 28, and the gasified refrigerant flows tothe evaporator 8 via the pressure equalizing pipe 29.

As described above, according to the present embodiment, the refrigerantand the lubricant which flow out of the oil tank 23 are supplied to thebuffer tank 28 via the pressure equalizing pipe 29, and the lubricant istemporarily stored in the buffer tank 28. In this manner, even if thefoaming occurs inside the oil tank 23 and the refrigerant and thelubricant flow out of the oil tank 23, the lubricant is stored in thebuffer tank 28, and does not flow to the refrigerating cycle. Only therefrigerant is guided toward the refrigerating cycle.

In addition, the lubricant having the dissolved refrigerant is suppliedto the separation region 41 of the oil tank 23, and the lubricant havingthe dissolved refrigerant is separated into the lubricant and therefrigerant in the separation region 41. Then, the separated lubricantis supplied from the separation region 41 to the discharge region 42,and is supplied into the housing 30. The separation region 41 and thedischarge region 42 are partitioned by the partition plate 43.Accordingly, in the separation region 41, the lubricant flowing into theoil tank 23 is efficiently separated using a specific gravity differencebetween the lubricant and the refrigerant or the increased temperatureof the lubricant in a narrow space. In addition, the partition plate 43is installed. Accordingly, even if the foaming phenomenon occurs in theseparation region 41, it is possible to prevent the lubricant having thebubbles formed therein from flowing into the discharge region 42.

According to the above-described configurations, it is possible toreduce the amount of the lubricant flowing out to the refrigeratingcycle such as the evaporator 8. The amount of the refrigerant suctionedby the oil pump 36 is reduced. Therefore, it is possible to prevent theamount of the lubricant circulating in the lubricant system from beingreduced.

REFERENCE SIGNS LIST

-   -   1: centrifugal chiller    -   2: turbo compressor    -   3: condenser    -   4: sub-cooler    -   5: first pressure-reducing valve    -   6: economizer    -   7: second pressure-reducing valve    -   8: evaporator    -   9: motor    -   10: motor shaft    -   10 a: one end    -   11: rotary shaft    -   11 a: one end    -   11 b: other end    -   12: first stage impeller    -   13: second stage impeller    -   14: rolling bearing    -   15: compression mechanism    -   17: gear    -   18: gear    -   19: acceleration mechanism    -   20: stator    -   21: rotor    -   22: lubricant supply line    -   23: oil tank    -   24: oil cooler    -   25: lubricant discharge line    -   26: return pipe    -   27: heater    -   28: buffer tank    -   29: pressure equalizing pipe    -   30: housing    -   31: motor housing    -   32: accelerator housing    -   33: compressor housing    -   34: refrigerant supply line    -   35: temperature measuring unit    -   36: oil pump    -   41: separation region    -   42: discharge region    -   43: partition plate    -   44: flow forming plate

1. A chiller comprising: a refrigerating cycle that includes an electriccompressor having a compression mechanism driven by a motor, acondenser, and an evaporator, and in which a refrigerant is circulated;an oil tank that stores a lubricant; a heater that is installed insidethe oil tank so as to heat the lubricant; an oil circulation pipe thatis connected to the oil tank so as to supply the lubricant from the oiltank into a housing for accommodating the motor and to return thelubricant from the housing to the oil tank; a pressure equalizing pipe,one end of which is connected to the oil tank, separately from the oilcirculation pipe, and the other end of which is connected to therefrigerating cycle; and a buffer tank that is installed in the pressureequalizing pipe, and that receives the refrigerant and the lubricantwhich flow out of the oil tank so as to store the lubricant.
 2. Thechiller according to claim 1, further comprising: a return pipe, one endof which is connected to the buffer tank, and the other end of which isconnected to the oil tank, separately from the pressure equalizing pipe,and that returns the lubricant stored in the buffer tank to the oiltank.
 3. The chiller according to claim 2, wherein a position where thereturn pipe is connected to the oil tank is in the vicinity of aposition where the oil circulation pipe is connected to the oil tank. 4.The chiller according to claim 1, wherein the oil tank is partitioned bya partition plate, and is divided into a separation region into whichthe lubricant returned from the housing flows, and a discharge regionthrough which the lubricant is supplied to the housing.
 5. The chilleraccording to claim 4, wherein a flow forming plate for guiding a flow ofthe lubricant stored in the oil tank from an upper portion toward alower portion or from the lower portion toward the upper portion isinstalled in the separation region.
 6. The chiller according to claim 4,wherein the partition plate is installed away from a bottom surface ofthe oil tank.
 7. The chiller according to claim 2, wherein the oil tankis partitioned by a partition plate, and is divided into a separationregion into which the lubricant returned from the housing flows, and adischarge region through which the lubricant is supplied to the housing.8. The chiller according to claim 7, wherein a flow forming plate forguiding a flow of the lubricant stored in the oil tank from an upperportion toward a lower portion or from the lower portion toward theupper portion is installed in the separation region.
 9. The chilleraccording to claim 7, wherein the partition plate is installed away froma bottom surface of the oil tank.
 10. The chiller according to claim 3,wherein the oil tank is partitioned by a partition plate, and is dividedinto a separation region into which the lubricant returned from thehousing flows, and a discharge region through which the lubricant issupplied to the housing.
 11. The chiller according to claim 10, whereina flow forming plate for guiding a flow of the lubricant stored in theoil tank from an upper portion toward a lower portion or from the lowerportion toward the upper portion is installed in the separation region.12. The chiller according to claim 10, wherein the partition plate isinstalled away from a bottom surface of the oil tank.